CN114046957A - Three-dimensional shear layer correction method for open wind tunnel far field noise measurement - Google Patents

Three-dimensional shear layer correction method for open wind tunnel far field noise measurement Download PDF

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CN114046957A
CN114046957A CN202111356027.0A CN202111356027A CN114046957A CN 114046957 A CN114046957 A CN 114046957A CN 202111356027 A CN202111356027 A CN 202111356027A CN 114046957 A CN114046957 A CN 114046957A
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shear layer
wind tunnel
sound
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张军
陈正武
张俊龙
雷红胜
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Chengdu Fluid Power Innovation Center
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M9/00—Aerodynamic testing; Arrangements in or on wind tunnels
    • G01M9/02—Wind tunnels
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M9/00—Aerodynamic testing; Arrangements in or on wind tunnels
    • G01M9/06—Measuring arrangements specially adapted for aerodynamic testing
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M9/00—Aerodynamic testing; Arrangements in or on wind tunnels
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Abstract

The invention discloses a three-dimensional shear layer correction method for measuring far field noise of an open wind tunnel, which comprises the following steps of: step 1: obtaining local atmospheric environment parameters, and calculating a sound velocity c0 and an incoming flow Mach number M; step 2: determining the coordinates of the observation points, and acquiring the position of the plane of the shear layer of the open wind tunnel; and step 3: establishing a relational expression between angles in a vertical plane; and 4, step 4: solving the nonlinear equation set formed in the step 2 and the step 3 to obtain a corresponding angle value; and 5: calculating the sound wave propagation delay time from the sound source point in the jet flow to the measuring point outside the jet flow; step 6: calculating a sound pressure amplitude correction value of a jet flow external measurement point; and 7: and calculating the atmosphere to obtain a final sound pressure amplitude correction result. The method is suitable for the large-size opening wind tunnel with the rectangular nozzle section, takes the absorption effect of the atmosphere on sound waves with different frequencies into consideration, and has higher correction precision than the traditional two-dimensional method.

Description

Three-dimensional shear layer correction method for open wind tunnel far field noise measurement
Technical Field
The invention relates to the field of aerodynamics, in particular to a three-dimensional shear layer correction method for measuring far-field noise of an open wind tunnel.
Background
The aerodynamic noise problem must be considered in the design and development process of large civil passenger planes, high-speed ground vehicles and the like. The international civil aviation organization describes the noise limit values of the third stage and the fourth stage of airworthiness approval of various airplanes in an ICAO accessory 16 volume 1, and a new airplane type with unqualified noise cannot obtain airworthiness certification, so that the international market cannot be entered. The sound environment quality standard issued by China requires that the equivalent sound pressure level of the environmental noise at night in the areas on two sides of a railway and a trunk line cannot exceed 60dB, and a noise pollution prevention method is correspondingly issued.
The acoustic wind tunnel is an efficient test research platform for solving the problem of aerodynamic noise of airplanes, high-speed ground vehicles and the like. In order to identify and evaluate the aerodynamic noise generated by airplanes, high-speed trains and the like, an efficient aerodynamic noise testing technology needs to be developed according to the characteristics of the acoustic wind tunnel to accurately measure the noise source distribution and the far-field sound pressure level. Pneumatic noise tests are typically performed in the acoustic wind tunnel opening test section, with the microphone array or far field microphone placed outside the airflow for far field noise measurements (source-to-point distances greater than 10 wavelengths). Thus flow noise generated by the interaction of the airflow with the microphone can be avoided, but the acoustic waves generated by the test model need to pass through the shear layer of the wind tunnel jet before reaching the microphone. The jet flow shear layer is formed by shear force between wind tunnel core jet flow and surrounding static air, and the flow velocity in the shear layer is changed in a certain rule (see figure 1). The sound waves passing through the shear layer are affected by various propagation effects such as reflection, refraction and scattering, and the phase and amplitude characteristics of the sound waves are changed accordingly. If the shear layer correction is not performed, then the far field noise measurement will be "inaccurate".
For the correction of the jet flow shear layer of the open wind tunnel at home and abroad, a two-dimensional correction method (called an Amiet method for short) provided by an Amiet scholars in the last century is generally adopted. The method mainly aims at the acoustic wind tunnel with a round nozzle section, namely, the geometric form of a shear layer is not changed from a sound source point in jet flow to any measuring point outside the jet flow. Obviously, for acoustic wind tunnels of the non-circular jet type, for example with a rectangular cross-section of the jet, the Amiet method is not strictly applicable. When the wind tunnel nozzle is small in size and the test section is short, errors caused by the Amiet method are not obvious. However, a plurality of large aeroacoustics wind tunnels are built in China, the size of the wind tunnel nozzle reaches several meters, the length of the test segment reaches several tens of meters, and if the shearing layer effect is corrected by still adopting the Amiet method, a large error is generated. The wind tunnel shear layer correction methods proposed in recent years can be roughly classified into two types: the methods for calculating the pneumatic acoustics class and the empirical formula class either need to carry out a large amount of complicated calculation and are time-consuming or have poor correction precision. Therefore, in order to effectively improve the precision of test identification and evaluation such as far field noise directivity evaluation, far field noise level standard evaluation and the like in the pneumatic noise wind tunnel test process of airplanes, high-speed trains, automobiles and the like, a new three-dimensional shear layer correction method needs to be developed.
Disclosure of Invention
The invention aims to solve the problems in the prior art and provides a three-dimensional shear layer correction method for measuring far-field noise of an open wind tunnel, which can obviously improve correction precision when applied.
The purpose of the invention is mainly realized by the following technical scheme:
a three-dimensional shear layer correction method for measuring far field noise of an open wind tunnel is characterized by comprising the following steps:
step 1: obtaining local atmospheric environment parameters: calculating sound velocity c0 and an incoming flow Mach number M by using pressure P0, temperature T0, relative humidity q and wind tunnel velocity pressure Pv;
step 2: setting a sound source point position as an original point, determining the coordinate of an observation point, and acquiring the position of the plane of the shear layer of the open wind tunnel;
and step 3: establishing a measurement angle theta in a vertical planemConvection angle theta, emission angle theta' and refraction angle theta0The relation between them, and the measurement angle theta in the horizontal planemAngle of convection Θ, angle of emission Θ', and angle of refraction Θ0The relation between;
and 4, step 4: solving the nonlinear equation set formed in the step 2 and the step 3 to obtain a corresponding angle value;
and 5: calculating the sound wave propagation delay time delta t from the jet flow internal sound source point to the jet flow external measuring point;
step 6: calculating a sound pressure amplitude correction value Pc/Pm of a measurement point outside the jet flow;
and 7: calculating the absorption effect alpha of the atmosphere on the sound wave to obtain the final sound pressure amplitude correction result Pc。
Further, in the step 2, a laser distance meter is used for measurement, and the linear distance R from the sound source point to the measurement point is obtainedmHorizontal distance R from the source point to the shear layertHorizontal distance R of shear layer to measuring surfacedThe distance h from the viewpoint to the horizontal plane.
Further, the horizontal plane passes through the intersection point of the sound source-measuring point connecting line and the shear layer, and the position of the shear layer plane is considered to be coincident with the position of the extension line of the wind tunnel nozzle, so that the position of the shear layer plane is determined.
Further, the calculation of the nonlinear equation set in the step 4 adopts a global Newton method, and the angle theta is measuredmAnd thetamAs an initial value.
Further, the calculation of the nonlinear equation system in the step 4 adopts a table lookup method.
Further, the "table lookup method" limits the range of the emission angle Θ 'to 20 ° -160 °, and values are obtained at intervals of 0.5 °, where Θ' is 20 °,20.5 °,.
Further, the absorption α of the sound wave by the atmosphere in the step 7 includes a viscous heat absorption, a relaxation absorption of an oxygen atom, and a relaxation absorption of a nitrogen atom, where α ═ αT+αO+αN。
During the experiment, firstly, an environment testing instrument is used for obtaining the local atmospheric pressure P in the wind tunnel test section0Temperature T0Accurate reading of air relative humidity q and the like, and wind tunnel speed pressure P is obtained through a pitot tube arranged at an outlet of a wind tunnel contraction sectionv. Then, the sound velocity c is calculated0And the incoming flow mach number M. By the position of the potential sound source point at the test modelObtaining the linear distance R from the sound source point to the outer measuring point of the jet flow by a laser range finder as the originmHorizontal distance R from the source point to the shear layer planetHorizontal distance R between shear layer plane and measuring surfacedAnd the distance h between the observation point and a certain horizontal plane (the horizontal plane passes through the intersection point of the sound source-measuring point connecting line and the shear layer plane), so that the coordinates (x, y, z) of the observation point are calculated.
The invention has the advantages that: the three-dimensional shear layer correction method is suitable for large-scale open wind tunnels with rectangular nozzle sections, takes the absorption effect of atmosphere on sound waves with different frequencies into consideration, and can simultaneously correct the delay time and the sound pressure amplitude of the sound waves.
Drawings
The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention.
In the drawings:
1. an internal jet sound source; 2. a jet flow outer microphone; 3. a shear layer; 4. opening a wind tunnel nozzle; 5. an open wind tunnel collector.
FIG. 1 is a schematic view of an open wind tunnel shear layer modification;
FIG. 2 is a schematic view of an open wind tunnel shear layer modified acoustic wave propagation geometry;
FIG. 3 is a schematic diagram of a shear layer modified geometry according to an embodiment;
FIG. 4 illustrates the results of the correction of acoustic propagation delay time through the shear layer;
FIG. 5 illustrates the sound pressure amplitude correction result of the shear layer;
FIG. 6 is a graph showing the relative difference between the three-dimensional shear layer modification and the Amiet method, and the phase modification in comparative example 1;
FIG. 7 is a graph showing the relative difference between the three-dimensional shear layer modification and the Amiet method and the sound pressure amplitude modification in comparative example 1.
Detailed Description
The following description of the embodiments of the present invention is provided to facilitate the understanding of the present invention by those skilled in the art, but it should be understood that the present invention is not limited to the scope of the embodiments, and it will be apparent to those skilled in the art that various changes may be made without departing from the spirit and scope of the invention as defined and defined in the appended claims, and all matters produced by the invention using the inventive concept are protected.
The invention discloses a three-dimensional shear layer correction method for measuring far field noise of an open wind tunnel, which comprises the following steps of:
step 1: obtaining local atmospheric environment parameters: pressure P0Temperature T0Relative humidity q and wind tunnel velocity pressure PvCalculating the speed of sound c0And the incoming flow mach number M.
Local atmospheric environmental parameter P0、q、T0The weather parameter is measured by an experimental instrument or obtained by inquiring the weather parameters of a local area through a network. According to wind tunnel velocity pvMach number M of the incoming flow, sound velocity c0By the formula
Figure BDA0003357120790000041
Figure BDA0003357120790000042
The calculation was carried out with γ being 1.4 and R being 287.09.
Step 2: and setting the position of a sound source point as an original point, determining the coordinate of an observation point through a geometric relation, and acquiring the position of the plane of the shear layer of the open wind tunnel.
As shown in FIG. 2, the coordinates of the source point are (0, 0, 0), the coordinates of the observation point are (x, y, z), and the linear distance R from the sound source point to the measuring point outside the jet flow is obtained by the laser distance measuring instrumentmHorizontal distance R from the source point to the shear layer planetHorizontal distance R between shear layer plane and measuring surfacedThe distance h between the observation point and a horizontal plane (the horizontal plane passes through the intersection point of the sound source-measuring point connecting line and the shear layer plane).
The linear distance from the sound source point to the observation point can be obtained according to the geometric relationship
Figure BDA0003357120790000043
y＝Rt+Rd，z＝h(1+Rd/Rt). Will measure to obtain Rm，Rt，RdThe value of h is then calculated according to the above formula (x, y, z).
In the invention, the method for acquiring the position of the shear layer plane comprises the following steps: and measuring a flow field by instruments such as a hot wire anemometer, a pitot tube and the like to obtain an open wind tunnel shear layer area, wherein the shear layer plane is positioned at a half-speed point in the area.
In engineering, the plane of the extension line of the wind tunnel nozzle can be directly considered as a shear layer plane.
And step 3: establishing a measurement angle theta in a vertical planemConvection angle theta, emission angle theta' and refraction angle theta0The relation between them, and the measurement angle theta in the horizontal planemAngle of convection Θ, angle of emission Θ', and angle of refraction Θ0The relation between:
Figure BDA0003357120790000044
Figure BDA0003357120790000051
Figure BDA0003357120790000052
Figure BDA0003357120790000053
the angle in the vertical plane satisfies the following relation:
Figure BDA0003357120790000054
Figure BDA0003357120790000055
Figure BDA0003357120790000056
Figure BDA0003357120790000057
Figure BDA0003357120790000058
Figure BDA0003357120790000059
Figure BDA00033571207900000510
and 4, step 4: and (4) solving the nonlinear equation set formed in the step (2) and the step (3) to obtain a corresponding angle value.
In the invention, the calculation of the nonlinear equation system adopts a global Newton method, and the angle theta is measuredmAnd thetamAs an initial value.
In the invention, the calculation of the nonlinear equation system can also adopt a table query method, and the steps are as follows:
in step 1, the emission angle Θ 'is limited to 20 ° -160 ° and is set at 0.5 ° intervals, where Θ' is 20 °,20.5 °, as well as 281 ° in total. Substituting the given value theta 'into a formula (3) to obtain theta';
step 2, giving theta 'and theta', and obtaining theta through a formula (6);
step 3, setting theta 'and theta', and obtaining theta through a formula (8)0；
Step 4, give theta0θ is obtained by the formula (9)0；
Step 5, give theta and theta0Theta is obtained by the formulas (10) and (11)mAnd x;
step 6, given x, obtaining theta through formula (1)m。
And 6, repeating the steps 1-6 until the calculation of other angle values of all initial inputs of theta' is completed. Further, a data table is obtained, where column 1 is ΘmThe 2 nd column is thetamColumns 3-6 are theta, theta0，Θ′，θ0。
Step 7, during the actual measurement process, according to (theta)m，θm) The value of (a) is obtained by inquiring theta according to the principle of proximity0，Θ′，θ0The value of (c). The method can greatly accelerate the calculation speed.
And 5: and (3) calculating the sound wave propagation delay time delta t from the sound source point in the jet flow to the measuring point outside the jet flow according to the formula (12).
Figure BDA0003357120790000061
Step 6: calculating sound pressure amplitude correction value P of external jet flow measurement pointc/PmThe calculation is performed according to the formula (13).
Figure BDA0003357120790000062
Therein, ζ2＝(1-M·cosΘ0)2-cos2Θ0,
Figure BDA0003357120790000063
Figure BDA0003357120790000064
JM＝h2sinΘ0sinθ0(A1A2+A3A4)
Figure BDA0003357120790000065
Figure BDA0003357120790000071
Figure BDA0003357120790000072
Figure BDA0003357120790000073
And 7: the absorption effect of the atmosphere on the sound wave is taken into account to obtain the final sound pressure amplitude correction result Pc. The atmospheric absorption includes a viscous heat absorption, a relaxation absorption of oxygen atoms, and a relaxation absorption of nitrogen atoms, and is calculated according to formula (14):
α＝αT+αO+αN (14)
Figure BDA0003357120790000074
Figure BDA0003357120790000075
Figure BDA0003357120790000076
Figure BDA0003357120790000077
Figure BDA0003357120790000078
wherein, P0Is at standard atmospheric pressure, T0293.15K is the reference temperature and q is the relative humidity. Finally, the sound pressure amplitude after being corrected by the shear layer is Pc＝α·r·Pc. Wherein the content of the first and second substances,
Figure BDA0003357120790000079
is the actual propagation distance of the sound ray from the sound source to the measurement point.
And (4) calculating the delay time delta t and the sound pressure amplitude correction quantity delta p after the shear layer correction according to the steps 1-7.
Example 1
The relative position of the sound source 1 and the microphone array within the jet is shown in figure 3. In an open wind tunnel with a rectangular section of a nozzle 4 of the open wind tunnel and the size of 5.5m (width) multiplied by 4m (height), a shear layer 3 is positioned on an extension line of the nozzle 4 of the open wind tunnel, and a jet internal sound source 1 is positioned at xs＝[0m，0m，0m]The aperture of the microphone 2 array outside the jet flow is 3m and is positioned in the upstream direction of the sound source, the distance from the center of the microphone 2 array outside the jet flow to the sound source 1 is 2m and is on the same straight line with the sound source 1, the distance between the sound source surface and the array surface is 4m, and the wind speed is 80 m/s.
The three-dimensional shear layer correction method for the open wind tunnel aerodynamic noise measurement comprises the following steps:
step 1: recording local atmospheric pressure p by instrument0Temperature T0Relative humidity q of air and wind tunnel velocity Pv. According to the formula
Figure BDA0003357120790000081
Calculating the speed of sound c0And the incoming flow mach number M.
Step 2: measuring with laser distance meter to obtain linear distance R from sound source point to measuring pointmHorizontal distance R from the source point to the shear layertHorizontal distance R of shear layer to measuring surfacedThe distance h from the source point to a horizontal plane (which passes through the intersection of the source-measurement point line and the shear layer). The location of the shear layer plane is determined by considering the location of the shear layer plane coincident with the extension of the wind tunnel jet. According to the formula y ═ Rt+Rd，z＝h(1+Rd/Rt)，
Figure BDA0003357120790000082
The coordinates (x, y, z) of the measurement point are calculated.
And step 3: according to the geometrical relationship among the sound source point, the measuring point and the position of the shear layer plane, establishing a measuring angle theta in the vertical plane according to the formulas (1) to (4)mConvection angle theta, emission angle theta' and refraction angle theta0The relational expression (c) of (c). Establishing a measurement angle theta of (XOY) in the horizontal plane according to the formulas (5) to (1)mAngle of convection Θ, angle of emission Θ', and angle of refraction Θ0The relational expression (c) of (c).
And 4, step 4: and calculating a nonlinear equation system comprising 8 angles by a Newton iteration method to obtain 8 angle values in a horizontal plane and a vertical plane. (ii) a
And 5: the acoustic wave propagation delay time Δ t from the in-jet acoustic source point to the out-of-jet measurement point is calculated according to equation (12).
Step 6: calculating (13) a sound pressure amplitude correction value P of the external measurement point of the jet flow according to a formulac/Pm。
And 7: calculating the atmospheric sound absorption coefficient alpha according to the formulas (14) to (19) to obtain the final sound pressure correction value Pc＝α·r·Pc。
Example 2
The relative position of the sound source 1 and the microphone array within the jet is shown in figure 3. In an open wind tunnel with a rectangular section of a nozzle 4 of the open wind tunnel and the size of 5.5m (width) multiplied by 4m (height), a shear layer 3 is positioned on an extension line of the nozzle 4 of the open wind tunnel, and a jet internal sound source 1 is positioned at xs＝[0m，0m，0m]The aperture of the microphone 2 array outside the jet flow is 3m and is positioned in the upstream direction of the sound source, the distance from the center of the microphone 2 array outside the jet flow to the sound source is 2m and is on the same straight line with the sound source, the distance between the sound source surface and the array surface is 4m, and the wind speed is 80 m/s.
The three-dimensional shear layer correction method for the open wind tunnel aerodynamic noise measurement comprises the following steps:
step 1: recording local atmospheric pressure p by instrument0Temperature T0Relative humidity q of air and wind tunnel velocity Pv. According to the formula
Figure BDA0003357120790000091
Calculating the speed of sound c0And the incoming flow mach number M.
Step 2: measuring with laser distance meter to obtain linear distance R from sound source point to measuring pointmHorizontal distance R from the source point to the shear layertHorizontal distance R of shear layer to measuring surfacedThe distance h from the source point to a horizontal plane (which passes through the intersection of the source-measurement point line and the shear layer). The location of the shear layer plane is determined by considering the location of the shear layer plane coincident with the extension of the wind tunnel jet. According to the formula y ═ Rt+Rd，z＝h(1+Rd/Rt)，
Figure BDA0003357120790000092
The coordinates (x, y, z) of the measurement point are calculated.
And step 3: according to the geometrical relationship among the sound source point, the measuring point and the position of the shear layer plane, establishing a measuring angle theta in the vertical plane according to the formulas (1) to (4)mConvection angle theta, emission angle theta' and refraction angle theta0The relational expression (c) of (c). Establishing a measurement angle theta of (XOY) in the horizontal plane according to the formulas (5) to (1)mAngle of convection Θ, angle of emission Θ', and angle of refraction Θ0The relational expression (c) of (c).
And 4, step 4: through a table query method, a nonlinear equation system containing 8 angles is calculated, and 8 angle values in a horizontal plane and a vertical plane are obtained.
And 5: the acoustic wave propagation delay time Δ t from the in-jet acoustic source point to the out-of-jet measurement point is calculated according to equation (12).
Step 6: calculating (13) a sound pressure amplitude correction value P of the external measurement point of the jet flow according to a formulac/Pm。
And 7: calculating the atmospheric sound absorption coefficient alpha according to the formulas (14) to (19) to obtain the final sound pressure correction value Pc＝α·r·Pc。
Analysis of the results of example 1 and example 2:
as shown in fig. 4 and 5, the sound wave propagation delay time and sound pressure level correction on the array surface of the fluidic outer microphone are shown.
Under the action of convection effect and refraction effect, the more upstream, the longer the delay time of the sound wave is; the more downstream the acoustic wave is, the smaller the delay time. As the wind speed increases, the delay time value at the same position on the array plane increases. For the relative position relationship in fig. 3, the difference between the delay times of the most upstream and the most downstream on the array plane can reach 4ms at the common test wind speed. This shows that for sound waves above 250Hz, the relative phase difference of the microphones at extreme positions on the array plane can reach 360 degrees. When the sound wave encounters vortices of different scales in the shear layer during the propagation process, a considerable random phase error is generated on the array surface, thereby causing difficulty in accurate identification of the sound source. Fig. 5 shows the variation of the sound pressure amplitude correction amount on the microphone array surface with the wind speed. Since the microphone is located upstream of the source, the sound pressure amplitude correction on the array plane is always greater than zero, indicating that the measured value of the sound pressure outside the jet is smaller than the actual value. According to the calculation result, the correction amount of the sound pressure amplitude is larger the further upstream. Under the condition of the wind speed of 80m/s, the sound pressure amplitude correction quantity on the microphone array surface can reach more than 2 dB.
Comparative example 1
Aiming at the working conditions in the embodiment, a three-dimensional correction method and an Amiet method are adopted to calculate the relative difference between the propagation delay time of the sound wave passing through the shear layer and the sound pressure amplitude correction. And selecting the position of the sound source as xs ═ 0m,0m,0m, and the position of the microphone as xm [ -5:5m,3m,4.5m ].
And (4) analyzing results:
fig. 6 and 7 are relative differences calculated for the delay time and the sound pressure amplitude. In fig. 6, the curves correspond to, from top to bottom, M ═ 0.29, M ═ 0.26, M ═ 0.23, M ═ 0.20, M ═ 0.17, and M ═ 0.15. Theta in FIG. 7mThe 40 ° position curve corresponds to M ═ 0.29, M ═ 0.26, M ═ 0.23, M ═ 0.20, M ═ 0.17, M ═ 0.15, and Θ is plotted from top to bottom in sequencemThe 140-degree position curve corresponds to M-0.29, M-0.26, M-0.23 and,M＝0.20、M＝0.17、M＝0.15。
Curves with different thicknesses and different linear shapes in the graph represent different incoming flow Mach numbers, the delay time calculation error between the Amiet method and the three-dimensional correction method is minimum near 90 degrees (a sound source-microphone connecting line is vertical to a shear layer), and the relative difference value between the Amiet method and the three-dimensional correction method is increased along with the movement of an observation point to the upstream direction or the downstream direction of the wind tunnel. Under the condition of the wind speed of 60m/s, the relative difference of the delay time around the measuring angle of 40 degrees or 140 degrees can reach 5 percent.

Claims (7)

1. A three-dimensional shear layer correction method for measuring far field noise of an open wind tunnel is characterized by comprising the following steps:
step 1: obtaining local atmospheric environment parameters: calculating sound velocity c0 and an incoming flow Mach number M by using pressure P0, temperature T0, relative humidity q and wind tunnel velocity pressure Pv;
step 2: setting a sound source point position as an original point, determining the coordinate of an observation point, and acquiring the position of the plane of the shear layer of the open wind tunnel;
and step 3: establishing a measurement angle theta in a vertical planemConvection angle theta, emission angle theta' and refraction angle theta0The relation between them, and the measurement angle theta in the horizontal planemAngle of convection Θ, angle of emission Θ', and angle of refraction Θ0The relation between;
and 4, step 4: solving the nonlinear equation set formed in the step 2 and the step 3 to obtain a corresponding angle value;
and 5: calculating the sound wave propagation delay time delta t from the jet flow internal sound source point to the jet flow external measuring point;
step 6: calculating a sound pressure amplitude correction value Pc/Pm of a measurement point outside the jet flow;
and 7: calculating the absorption effect alpha of the atmosphere on the sound wave to obtain the final sound pressure amplitude correction result Pc。
2. The three-dimensional shear layer correction method for open wind tunnel far field noise measurement according to claim 1, characterized in that: in the step 2, a laser range finder is used for measurement to obtain the distance from the sound source point to the measurement pointLinear distance R ofmHorizontal distance R from the source point to the shear layertHorizontal distance R of shear layer to measuring surfacedThe distance h from the viewpoint to the horizontal plane.
3. The three-dimensional shear layer correction method for open wind tunnel far field noise measurement according to claim 2, characterized in that: the horizontal plane passes through the intersection point of the sound source-measuring point connecting line and the shear layer, and the position of the shear layer plane is considered to be coincident with the position of the extension line of the wind tunnel nozzle, so that the position of the shear layer plane is determined.
4. The three-dimensional shear layer correction method for open wind tunnel far field noise measurement according to claim 3, characterized in that: the calculation of the nonlinear equation set in the step 4 adopts a global Newton method to measure the angle thetamAnd thetamAs an initial value.
5. The three-dimensional shear layer correction method for open wind tunnel far field noise measurement according to claim 3, characterized in that: the calculation of the nonlinear equation system in the step 4 adopts a table query method.
6. The three-dimensional shear layer correction method for open wind tunnel far field noise measurement according to claim 5, characterized in that: the "table lookup method" limits the range of the emission angle Θ 'to 20 ° -160 ° and takes values at intervals of 0.5 °, and Θ' is 20 °,20.5 °,. and 160 °, for a total of 281 values.
7. The three-dimensional shear layer correction method for open wind tunnel far field noise measurement according to claim 6, characterized in that: the absorption α of the sound wave by the atmosphere in the step 7 includes a viscous heat absorption, a relaxation absorption of an oxygen atom, and a relaxation absorption of a nitrogen atom, where α ═ αT+αO+αN。
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